With rapid development of three-dimensional computer graphics technology in recent years, image synthesis is enabled at a level approaching or equaling photographed images. Especially, image synthesis is being actively used for design visualization using various advanced materials in fields of, e.g., mobile phones, home electronics, fashion, cars and architecture, and used in image special effect fields requiring synthesis with real pictures. However, in order to produce such images, very long computing time and designer's working time are still required. Thus, a lot of researches and technical developments are being made to solve this problem.
Surface materials of scene elements are one of important factors determining reality of CGI (Computer Generated Imagery). Especially, there are many things to be taken into consideration in order to render materials whose surface physical phenomenon is complex, e.g., body parts such as skin and hair, delicate cloths, mixed paint. An object coated with such materials may change in surface color or brightness depending on a direction in which the object is viewed (viewpoint direction) and a direction in which light is irradiated (light source direction). In particular, it is important to render properties information of a material having a complex directionality.
Various techniques have been developed to render the properties information. For example, a surface of a real object is photographed to obtain properties of its material as raw data. Also, a physical model and/or an empirical model are established and expressed in mathematical equations. However, there is a problem that, although the raw data can accurately render the properties of surface materials, its size is too big to be used in a network render farm environment using hundreds to thousands of CPUs (Central Processing Units). Further, not only there is a limitation in rendering delicate surface materials properties only by using a mathematical equation based model, but also the amount of calculation increases.
It is also important to edit and modify existing material information or produce a new material. This is because various experiments may be made on measured materials for improvements by using the measured materials properties only as reference data. To this end, an editing system supporting mixing of materials is required.
In general, detailed materials properties information has a large volume or requires a large amount of computation. Therefore, there is a demand for a method in which precise material information is used in a highly visible and large area while simplified material information is used in a poorly visible and small area. For this, it is necessary to support material information in a multi-resolution way.
Regarding this, related researches on, e.g., BRDF (Bi-directional Reflectance Distribution Function), BTF (Bi-directional Texture Function) and PTM (Polynomial Texture Map), are being conducted.